Error 130 dives on Fake Nitrox

[Eric Sedletzky]

Sure, so what? As divers we're not supposed to depend on others for our own safety. Something within this diver control should have caught this.

Exactly correct.
Each and every diver is solely responsible for one’s self regardless of borrowed or rented gear.
Learn to use every single piece if gear before you use it and if you can’t figure it out, learn to figure it out before you use it.
You have to wonder how many accidents happen because of unfamiliar gear?

 

[boulderjohn]

Is buddy support not one of the primary tenants of OW instruction? How many OW divers do you see with redundant gas supplies? @boulderjohn often mentions education theory and that students should only be taught what they NEED to know at that point. Otherwise, you risk them being confused about some topic that is truly necessary.

Yes, it is bad policy to teach stuff that people don't need to know for a course because it interferes with their ability to learn what they do need to know. The buddy system and the ability to use the resources of a dive buddy are considered to be essential skills, so they are very much pert of the training.

At the same time, we want divers to be able to handle situations where they (for one reason or another) do not have a buddy nearby. You want to have a buddy, but at the same time you should assume you can handle a situation without one. That is emphasized in tech diving. You are part of a team and have that resource, but you should always dive with the belief that you can handle things on your own if you have to. You will gladly use the team ini an emergency, but you don't depend upon it.

Not all agree. I was a UTD diver from almost the very beginning of that agency. I was told they at first had trouble getting insurance because their OW course did not include the CESA or other emergency swimming ascents. They finally prevailed because they said that UTD divers are so committed to team diving (the name means Unified Team Diving) that they would never, ever be in a situation where an emergency ascent was needed.

 

[boulderjohn]

Well I had a customer ask me for a 40% Nitrox mix because he wanted to go to 40m......and he was certified!!

As a career educator, I assure you that in all educational situations in all fields of study, there are occasionally students who do not recall every single detail of the courses they passed. And yes, some of them have absurd memory failures like that.

I once did a scuba refresher for a woman who had completed a couple hundred dives and was preparing for a dive trip after not diving for one year. I assumed she would not need much of a refresher, and in the water I was certainly right--she was very skilled, and I skipped all the refresher skills and worked on more advanced techniques.

However....

When she set up her gear at the beginning of class and turned on her air, she looked at her air integrated (via a hose) computer and noted that the computer had successfully analyzed the nitrox in the tank as 32%. Say what? I told her the computer cannot analyze the gas, and I told her there was just plain air in that tank. She insisted--her computer could analyze oxygen content, so the gas in that tank MUST be 32% nitrox. I told her that the shop only had an air compressor, and when they want nitrox, the ask me (the tech instructor) to make it for them using my own oxygen and my own equipment. I assured her I had not put nitrox in that tank. She was puzzled. She always asked for nitrox when she dived, and he computer had always analyzed it for her.

What had obviously happened is that at some point in the past she had correctly understood the process. She had analyzed the gas and set her computer. Then with big gaps in time between dives. she got a little confused and thought the computer was doing the analysis. She had probably been reinforcing that mistake for years by not analyzing the nitrox they were giving her. When you think about it, the idea is not all that far fetched. It would be possible to make a dive computer that would do that.

 

[Dan G]

It certainly is possible that there was poor instruction that led this diver to misunderstanding how his computer works. It is also possible that some basic PDC use was addressed in his OW class, he simply forgot, and he hasn't taken a class that addressed any theory since his OW class. He also may have done his OW quite some time ago and used tables never having had any instruction for a PDC in a formal setting. Once he got the computer back from his friend who borrowed it, he should know to check the settings. Rather than blaming an agency, I see our friend as more "willfully ignorant" compared to poorly taught.

I thought "fake" nitrox for air dives was a quite popular way to tackle the famous over(?) conservatism of RGBM dive computers... I've seen it in use a couple of times over the years...

I think you may be referring to when people dive Nx but keep their computer set to air. It adds conservatism to the NDL calculations and is very safe as long as the diver knows their MOD, why MOD is important, and doesn't rely on their computer to tell then when they get to their MOD.

 

[inquis]

I think you may be referring to when people dive Nx but keep their computer set to air.

I've seen both practices. The one you describe adds conservatism. The other reduces conservatism, typically done to increase NDL on dive 2 or 3 when RGBM is overly upright compared to other computers. (The diver I saw doing the latter was matching the NDL of their primary/DSAT-based computer.)

 

[stepfen]

I think you may be referring to when people dive Nx but keep their computer set to air. It adds conservatism to the NDL calculations and is very safe as long as the diver knows their MOD, why MOD is important, and doesn't rely on their computer to tell then when they get to their MOD.

No. I'm referring to exactly the opposite. People who dive Suunto's (or other RGBM DCs) knowing that they are very conservative, in order to match the NDL of other divers' DC (who run eg Buhlmann) set their Suunto's to higher (than the actual) O2%, increasing the NDL !!!

Yes! I have seen it with my own eyes (and fount it very difficult to believe how stupid people can be). A very active fellow diver told me proudly once that she was doing this, following the suggestion of a "very good instructor" and good friend of hers who "knew what she was talking about". She was so proud that in this way she saved the money for a new DC, after she discovered how conservative their brand new Suunto's are and she was so convinced that this was something exceptionaly smart to do, that I didn't even bother to express my concerns. To be honest, she claimed to have several 100s of succesful dives like this, so if it works for her, who am I to disagree??

I have also seen the exact same "solution" being suggested to another fellow diver wondering about his Suunto's low NDL times, by more experienced divers in another LoB. That 2nd guy was more sceptical about how smart this solution is, hence he didn't adopt it on the spot - but I am not sure he won't consider it in the future.

 

[BoltSnap]

When you think about it, the idea is not all that far fetched. It would be possible to make a dive computer that would do that.

Ratio computers do that, since few years ago, you just connect the sensor to the computer and test the gas from the tank. The computer would set the o2 % automatically in the computer.

 

[FishWatcher747]

No. I'm referring to exactly the opposite. People who dive Suunto's (or other RGBM DCs) knowing that they are very conservative, in order to match the NDL of other divers' DC (who run eg Buhlmann) set their Suunto's to higher (than the actual) O2%, increasing the NDL !!!

This is called a work around. Happens in life all the time.

If anyone has done this comparing Buhlmann and RGBM and can provide their data it would be interesting. I have heard anecdodally of people setting their computer to about 26% nitrox to compensate for the difference.

 

[inquis]

I have heard anecdodally of people setting their computer to about 26% nitrox to compensate for the difference.

I sincerely hope not, as it's more complicated than a one-time adjustment will allow. Depth matters as does prior dives.

At 80 ft with no prior dives, RGBM matches GF x/95 at 28 mins. Using the nitrox fraction to go even less conservative seems like a really bad idea. I don't have an RGBM planner at the moment, but assuming the increase due to nitrox is comparable between the algorithms (to 35 mins), clean RGBM on 26% would be equivalent to GF x/107 on air. <yikes>

OTOH, at 50 ft the clean RGBM is very close to GF x/85 and 11 minutes shorter than x/95. I'd guess that RGBM configured for 24% is equivalent to GF x/95 on air and configured for 26% is equivalent to x/99 on air.

With prior dives, it's going to be a crap shoot to configure without a reference. I can kinda see matching your primary computer's NDL so you don't bend the RGBM backup (having taken both on prior dives). Beyond that, I'd say just sell it and get something more in line with your desired conservatism.